1. Field of the Invention
This invention relates to image processing apparatuses such as copiers and printers.
2. Related Background Art
An image forming apparatus of the pertaining type, a copier for copying original images on paper or like sheet, is well known in the art.
Such a copier is provided with an automatic density regulation function for obtaining a copy of an image of a constant density regardless of the density of the original image. For automatic density regulation, original scanning is effected to the density of an original prior to image formation (the scanning being hereinafter referred to as photometric scan). At this time, a control unit calculates original exposure lamp "on" voltage or the like according to original density data obtained by a density sensor. With the lamp held "on" using the "on" voltage, original scanning is effected for printing by irradiating a photosensitive drum with reflected light from the original (the scanning being hereinafter referred to as exposure scan). Subsequently, printing is effected using a well-known process of electrophotography.
For a control unit noted above, a microcomputer is used extensively.
The microcomputer in the control unit usually includes a ROM, which contains relation between density data and corresponding adequate lamp voltages. Thus, the optimum lamp voltage is determined from the density data.
In such prior art, the "relation between density data and adequate lamp voltage" is always given by a fixed curve. However, the relationship between density data and adequate lamp voltage can vary over time due to photosensitive drum sensitivity changes, density sensor sensitivity changes, or lamp illumination intensity changes.
For example, if the photosensitivity drum sensitivity is reduced, with the same original, i.e., with the same density data it is impossible to obtain a print image of adequate density unless the lamp voltage level is increased.